The main objective of this work is to further our understanding of mechanisms of development. In higher, multicellular organisms, including man, development consists of a large array of different interlocking phenomena and these can be experimentally analyzed using a number of different technical or methodological approaches. In this study, the cellular slime molds, which are primitive multicellular eukaryotes, have been chosen as experimental organisms. This is largely because, by their very simple development, they not only expose certain developmental processes with the utmost clarity, but also they are very easy to handle in the laboratory. Two particular developmental processes are the central concern of this proposed research: chemotaxis and differentiation. The two processes are related in that in Dictyostelium discoideum they are both induced by cyclic AMP. Our first question is how this substance can effect these two processes, and this has brought us into the matter of other substances that have similar action, and how they might be related to cyclic AMP and its action.